1. Field of the Invention
The present invention relates to a ferroelectric memory device and a method of forming the same.
2. Description of the Related Art
A ferroelectric substance is typically a substance exhibiting a spontaneous electric dipole, which may be reoriented by an applied external electric field. The orientation, or polarization, may remain to some degree even after the external electric field is removed. In addition, spontaneous polarization directions may be affected by changes of the external electric field. Representative ferroelectric substances include PZT: Pb(Zr,Ti)O3 (lead zirconate titanate), SBT: SrBi2Ta2O9, etc. In order to form a ferroelectric substance, it is advantageous if the substance, e.g., PZT or SBT, has a crystal structure known as a perovskite structure. In general, this structure may be obtained by forming a ferroelectric layer, heating the layer in an oxidizing ambient at a high temperature, e.g., 700° C., and then crystallizing the layer.
When a ferroelectric layer is etched, e.g., in a process for forming a ferroelectric memory device, the ferroelectric layer may be etch-damaged. This etch-damage may decrease a capacitance of the ferroelectric layer by inducing a pyrochlore phase when the ferroelectric layer is crystallized. This etch-damage may have a significant effect on the reliability of a ferroelectric memory device. Accordingly, in order to avoid or overcome the problem of etch-damage, device structures in which ferroelectric layers are not etched have typically been required. In device structures in which ferroelectric layers are not etched, the ferroelectric layer is typically formed to cover a lower electrode pattern and an interlayer insulating layer and then crystallized. However, when crystallization is performed on a ferroelectric layer formed on an interlayer insulating layer formed of, e.g., silicon oxide, lifting or a cracking may occur and a pyrochlore phase may be generated due to a reaction of the silicon oxide layer with the ferroelectric layer. In addition, if a ferroelectric layer is formed on a curved or non-planar lower structure, crystallization of the ferroelectric layer may not occur smoothly, thereby degrading the reliability of the resulting ferroelectric memory device.